in a sealed capsule with no ambient air influence. As soon as his oxygen supply diminishes, he will experience some discomfort, will suffer from fatigue and becomes irrational. If he is not supplied with oxygen soon, his physical and mental performance will be seriously affected. If the capsule is opened, and air is allowed to enter, a person can survive in relative comfort at LOWER altitudes. air pressure and air density is equal both inside and outside the capsule, the person inside the capsule will again experience discomfort and fatigue 10,000' to Headache, fatigue, deterioration 14,000' of physical and mental per- formance. 15,000' to Impairment of judgment, euphoria, 18,000' disregard for sensory percep- tions, poor coordination, sleep- iness, dizziness 20,000' to Same symptoms as 15,000' to 35,000' 18,000' but more pronounced 35,000' to Immediate unconsciousness 40,000' (with little or no warning) One solution would be to provide the person inside the capsule with supplemental oxygen. However, this is only a short term remedy. When the oxygen supply is exhausted, the crew member once again suffers from hypoxia. The easiest solution would be to keep the capsule at a LOWER altitude where normal activities can continue. This is not always practical. Per- haps if we take a look at the laws of physics, we might find a suitable solution. If we compress air, we can INCREASE its pressure and at the same time INCREASE its density. Thus, if we can compress ambient air and duct it into our capsule, we can produce an "artificial atmosphere" having the same pressure as that of a lower altitude, and thus provide the needed oxygen, regardless of altitude. Obviously, if we introduce compressed air into a sealed capsule, we will increase the pressure, and likewise the oxygen supply, but what happens to the capsule structure? If we OVER-pressurize the capsule, structural damage is likely to occur. To preclude this possibility, we need a means of controlling the pressure. We could provide a means to regulate the air entering the capsule; then the pressure would increase, but the air in the capsule would soon become depleted of oxygen since the air is not moving through the capsule. By adding an OUTFLOW VALVE to our capsule, we can regulate the pressure inside by controlling the outflow of air from the capsule, as well as exchanging the air in the capsule by creating air flow. To increase pressure, the OUTFLOW VALVE would close, and to DECREASE the pressure, the OUTFLOW VALVE would open. We can monitor the pressure inside our capsule by the use of a DIFFERENTIAL PRESSURE GAUGE. It would be referenced to the INSIDE pressure as well as the OUTSIDE pressure, so it would indicate the difference between the two references and thus show cabin differential pressure. The pressure in the capsule is now regulated by the position of the outflow valve. But what would happen if the outflow valve were to stick closed? One of two choices are available. First, we could turn off our compressor, which would eventually lead to our original problem--NO OXYGEN; or secondly, we could install a second outflow valve. This back-up outflow valve is referred to as the SAFETY VALVE. It is merely a redundant feature in our pressurization system for the purpose of insuring safety, and preventing serious damage to our capsule. Now that we can control the pressure in our capsule, what about the task of flying the aircraft? We need a means of automating and selecting our system pressure to relieve the flight crew of manual pressure regulation and monitoring. By adding a CONTROLLER, an ON-OFF SWITCH and a SAFETY SOLENOID in the system, automatic monitoring of pressure and safety is accomplished. The CONTROLLER permits selection of any desired cabin pressure between sea level and 10,000'. It monitors the pressure altitude inside the capsule, and at the same time, controls the outflow valve to a position that maintains a selected cabin pressure altitude. The SAFETY SOLENOID is controlled by an ON-OFF switch, which in turn, controls the safety valve. When the switch is in the "ONII position (PRESSURIZE MODE) the SAFETY SOLENOID is de-energized allowing the safety valve to close and the capsule will pressurize. With the switch in the 1I0FF" position, (NON-PRESSURIZE MODE) the SAFETY SOLENOID is energized, which allows the safety valve to open, thus DE-PRESSURIZING the capsul e. 1. WHAT IS CONSIDERED TO BE STANDARD DAY ATMOSPHERIC PRESSURE AT SEA LEVEL? A. 14.20 PSI, 28.90 IN. Hg. B. 14.70 PSI, 29.92 IN. Hg. C. 4.30 PSI, 8.87 IN. Hg. D. 14.75 PSI, 30.30 IN. Hg. A. As altitude increases, pressure increases B. As altitude decreases, pressure will remain the same C. As altitude increases, pressure decreases D. As altitude decreases, pressure decreases C. Safety valve D. Controller 4. WHAT ARE THE PRESSURE REFERENCES USED TO DETERMINE CABIN DIFFERENTIAL PRESSURE? C. Safety valve pressure and pitot pressure D. Outflow valve pressure and upper deck pressure A. Differential pressure gauge B. Cabin rate-of-climb indicator 6. WHAT PREVENTS ULTIMATE DAMAGE TO THE PRESSURIZED CAPSULE UNDER PRESSURIZED CONDITIONS? 7. WHAT COMPONENT IN THE PRESSURIZATION SYSTEM PHYSICALLY MOVES TO REGULATE CABIN PRESSURE? B. Safety valve C. Outflow valve C. Energized, safety valve open D. De-energized, safety valve closed As this point in your workbook, you should be fairly well acquainted with the pressurization system components and their immediate function. Under- standing WHY pressurization is important, gives you the basis from which the purpose of each component can be further detailed. Previously, we discussed the capsule in which pressurization took place. Let's take a closer look at this capsule, its boundaries, construction, and related components. The pressure capsule is the cabin area of the Pressurized Centurion bounded by the firewall on the front and extending to the aft cabin pressure bulkhead. The cabin floor, just aft of the rear doorpost, becomes the bottom boundary, while the outer skins compose the remainder of our IIsealed capsulell • Like the larger twin Cessnas, the Pressurized Centurion is built on a IIfail-safe construction principle. ll If anyone structural part in the pressure capsule should fail, the remainder of the capsule would remain intact and functional. Double-row riveting, back-to-back formers, added reinforcement members, and heavier-gauge channels are items that provide the necessary strength to withstand the internal forces of pressuriza- tion. This construction method gives the Pressurized Centurion the same exceptional safety margin as cabin-class twin-engine aircraft. Increased rel iabil ity, safety, and infinite service 1 ife are the resul ts of IIfail-safe ll construction. 1. Door Seal. 2. Window Seal (Foul Weather) 3. Windshield. Cabi n Pressure C) 1. Rivet 2. Retainer 2. Skin 3. Seal Cabin sealing is accomplished in the same manner as the larger twins. First, the skins and formers are aligned and held in place securely, while all holes are drilled and reamed. The skins are removed and sealant is uniformly applied to the bare formers, then the skins are reinstalled. While the sealant is still workable, the formers and skins are riveted in place, resulting in an air-tight assembly. Should repair to the cabin pressure capsule be necessary, detailed instructions are outlined in the Pressurized Centurion Service Manual. Special types of sealants are used in different areas of the pressure capsule, so consult the Service Manual for proper sealant usage. Not only does the pressure capsule require special sealing, but so does the cabin door and emergency exit. The seals are specially designed to provide pressure retention. They are inflated from the cabin side by pressurized air which enters through holes in the hollow seal. Inflating the seals causes them to expand against the cabin door, emergency exit and fuselage structure for positive sealing. Pressurization has necessitated other changes in the Pressurized Centuiron. Stronger doors, redundant safety latches, and changes in window design Where cables and rods exit the pressure capsule, special labyrinth seals are installed to limit the escape of pressurized air from the cabin. the "unpressuri zed mode", the seal is relaxed and wi 11 allow moi sture to drain from the fuselage. In the "pressurized mode", the seal expands and closes the drain holes to prevent loss of pressurization. 2-3 PRESSURE CAPSULE Pressurization begins with compressed air. The source of this compressed air is the exhaust-driven TURBOCHARGER, located on the lower right-hand side of the engine. The primary function of the turbocharger is to provide the engine with compressed air for high altitude operation. The turbocharger compresses air into the IIUPPER DECK SYSTEW, which is the duct system between the compressor section of the turbocharger and the throttle plate of the induction system. A portion of this IIUPPER DECK AIRII is extracted and routed to the cabin for pressurization. The SONIC VENTURI is the means by which air is extracted from the upper deck. It functions as a fixed bleed-air orifice (flow limiter) to limit the amount of air taken from the upper deck, to prevent a deficiency of air to the engine. Compressing the air causes the temperature of the air to increase. Thus the air from the compressor section is very warm. If this hot air were to be routed directly to the cabin, it would provide a source of heat for the cabin. If heating the cabin is NOT desired, the air can be cooled before entering the cabin by the HEAT EXCHANGER, located on the lower left-hand side of the engine compartment. The HEAT EXCHANGER operates like a radiator. Ambient air flows through the fins of the heat exchanger, around the core, and exhausts overboard. The cool ambient air has thereby cooled the air PRESSURE CAPSULE ~ OVERBOARD inside the core of the heat exchanger, and cool compressed air is allowed to enter the cabin. An air scoop in the lower forward left side of the nose structure, and an exhaust scoop located in the lower side cowl panel assures a high volume of ambient airflow through the heat exchanger. A valve is included as part of the heat exchanger installation to enable the pilot to select either warm or cool airflow through the heat exchanger. In the "warm" position, the valve directs heated air from the engine exhaust shroud through the heat exchanger. A PUSH-PULL control, labeled "CABIN HEAT" is located on the lower right side in the instrument panel. This control operates the "air selector" valve in the heat exchanger assembly for cabin temperature control. After passing through the heat exchanger, 'pressurized air is routed into the cabin through a MANUAL DUMP VALVE PLENUM, located on the forward side of the firewall. When the MANUAL DUMP VALVE is opened, the pressurized air is routed overboard. A push-pull control in the cabin gives the pilot this option. In the event contaminated air enters the cabin, the MANUAL DUMP VALVE should be opened to route the contaminated air overboard. With the MANUAL DUMP VALVE closed, pressurized air enters the cabin through a flapper-type INLET CHECK VALVE installed on the aft side of the MANUAL DUMP VALVE PLENUM. In the event of a loss of incoming pressurized air, the check valve will trap pressurized air in the cabin and prevent back- flow. Loss of pressurized air could be the result of an engine malfunction or if the MANUAL DUMP VALVE is opened. ¢ ¢ RAM AIR FLOW 11I11I1111111111I HEATED RAM AIR FLOW PRESSURIZED AIR FROM TURBOCHARGER PRESSURIZED AIR VENTING FROM CABIN ------- MECHANICAL CONNECTION PNEUMATIC CONNECTION PRESSURIZED AIR DUMP VALVE CONTROL HANDLE CABIN HEAT, DEFROSTER AND VENTILATING AIR CONTROLS TO TO CABIN PRESSURIZATION ALTITUDE SELECTOR SWITCH CONTROL After passing through the inlet check valve, the pressurized air enters a DIVERTER CHAMBER. A valve within the diverter assembly is operated by a push-pull control labeled FLOOR-DEFROST/OVERHEAD. The valve directs the airflow from the diverter assembly to either the floor registers or to the overhead outlets. When the "CABIN HEAT" control is in the "COOL" mode, the air may be ducted to both the floor registers and the overhead outlets. When the control is in the "CABIN HEAP mode, the warm air is ducted through the floor level outlets only. This is accomplished by an interconnect between the "FLOOR/OVERHEAD" control and the "CABIN HEAP control. DEFROST air to the windshield is taken from the floor level distribution system. Fresh air is routed into the cabin when pressurization is not in use. Leading edge openings located in the wings provide cool air which is ducted into the cabin through CABIN PRESSURE CHECK VALVES. There are two valves; one per wing, located above each of the two forward seats along the wing butt line. Their function is to provide fresh air when in the depressurized mode and to automatically close when the cabin is pressuri zed. PRESSURE CAPSULE .• DEPRESSURIZE PRESSURE ON CABIN PRESSURE .•. PRESSURIZE To this point, we have discussed how air is INTRODUCED into the cabin providing cabin pressurization. How pressurization is regulated and controlled will be the topic of the next discussion. To provide an effective means of controlling cabin pressurization, an OUTFLOW VALVE is installed in a recess in the upper aft cabin pressure bulkhead. By locating the outflow valve in the aft section of the cabin, we produce a more effective exchange of air. Air enters the front of the cabin and exits the rear. When the outflow valve is mentioned, the SAFETY VALVE should also be recalled. The function of the SAFETY VALVE is to relieve cabin pressure should the outflow valve malfunction. It is located next to the outflow valve on the aft cabin pressure bulkhead. It also incorpor- ates a means of keeping the cabin de-pressurized when pressurization is not desired. A SAFETY SOLENOID is incorporated in the SAFETY VALVE itself, thereby directly controlling the position of the safety valve. When the cabin pressurization switch located to the left of the controller is in the "0FF" position, the SAFETY SOLENOID is energized, opening the SAFETY VALVE, and thereby maintaining an unpressurized cabin. Conversely, when the switch is in the "0N" position, the safety solenoid is de-energized, allowing the safety valve to close and the cabin to pressurize. DO NOT CONFUSE THE TWO VALVES! The safety valve incorporates a safety solenoid and the outflow valve is connecteG ~l the con troll er by a polethylene tube. Both valves are accessible by removing the interior panel at the aft pressure bulkhead. A cabin pressurization CIRCUIT BREAKER is provided to protect the elec- trical portion of the pressurization system. To select cabin altitude and meter reference pressure to the outflow valve, a CONTROLLER is installed on the lower left instrument panel within easy reach of the pilot. This is the IIBRAINS" of the pressurization system . To monitor the pressurization system, there are two gauges that indi- cate cabin pressure altitude, cabin altitude rate~of~climb, and cabin differential pressure. .'I';:'~' "-',' '-' I '---TO PRESSURIZED AIR DUMP VALVE ......._---_._-_ _------------- .....--- •••••_..-_ ...- .--------- ._---9:..------- ... .- ------- ~~ ..,- --------------------,---------_. __ .._--~---- .. - .'" - ",.. ". ",' - ••....-.-::--...... ,.----"'\- 0 ". .. \..:"", ",.-.......- ..- :-""-'...-" . .~ : ' I.tf-, ~oJ.O .,',_ • :j..... t',' ..,,: ~\ .,/: ~t' ,,_ : \ ~,' : Ii ~" .~~ ,/:~ , : ./:.' :~ ,':: .~: ~~ I. ~ I : I ~.- ~ , ..•.. '..... ----, --'.- c::..,.' ',.-- , 0. '- .- '"-~ ..•.•• __.' I.·::;::---"-'~ ,'.---" ,.,~.;..." .•..- - I : _-.. ~.:...._ - .•.• ~_" .. , : ' I - ' ~ il ..: , ' '. ,,: . \ ••, t ~ ' :: • • " : :- " :/ " : '" , ....1 ~... ' " ,.,1:" ,~ \ ",' I,' : ~ ,It .",~ : : -- '-'. ~-_.~_.' :> _ •• - "~--"":-': CABIN ALTITUDE and DIFFERENTIAL PRESSURE are combined into one instrument. The large needle indicates cabin pressure altitude, or the artificial altitude created by the pressurization system. The smaller needle indicates cabin differential pressure. DIFFERENTIAL PRESSURE is the difference in pressure between the inside and outside of the pressure capsule. A source from each pressure is referenced to the differential pressure gauge. The MAXIMUM CABIN DIFFERENTIAL PRESSURE is indicated by a "red-l ine" at 3.35 PSI. The second instrument associated with cabin pressurization is the CABIN RATE-OF-CLIMB INDICATOR. It is located on the left side of the instrument panel above the dump valve control handle. It is vented directly to the cabin and senses changes in pressure within the ) cabin to show cabin rate-of-climb or descent. A CABIN ALTITUDE WARNING LIGHT is incorporated to indicate when the cabin pressure altitude reaches and exceeds 12,400 ± 100 ft. The light is controlled by a barometric pressure switch locateJ forward of the instru- ment panel. When this light illuminates, it reminds the pilot of OXYGEN REQUIREMENTS necessary when the cabin altitude is in excess of 12,400 ft. The switch will reset at an altitude of approximately 11,700 ft. 1. WHAT PREVENTS PRESSURIZED AIR FROM ESCAPING PAST THE CABIN DOOR AND EMERGENCY EXIT? A. Rubber o'ring seals B. Seals inflated by upper deck pressure C. Hollow rubber seals inflated by cabin pressure D. Solid rubber seals 2. WHAT LIMITS PRESSURIZED AIR FROM ESCAPING AROUND CONTROL CABLES GOING THROUGH THE PRESSURE CAPSULE? C. Dyno-seals D. Labyrinth seals C. Heat air for the cabin only D. Cool air for the cabin only
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